// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_EVENTS_GESTURE_DETECTION_VELOCITY_TRACKER_H_
#define UI_EVENTS_GESTURE_DETECTION_VELOCITY_TRACKER_H_

#include <stdint.h>

#include "base/macros.h"
#include "base/memory/scoped_ptr.h"
#include "base/time/time.h"
#include "ui/events/gesture_detection/bitset_32.h"

namespace ui {

class MotionEvent;
class VelocityTrackerStrategy;

namespace {
    struct Estimator;
    struct Position;
}

// Port of VelocityTracker from Android
// * platform/frameworks/native/include/input/VelocityTracker.h
// * Change-Id: I4983db61b53e28479fc90d9211fafff68f7f49a6
// * Please update the Change-Id as upstream Android changes are pulled.
class VelocityTracker {
public:
    enum {
        // The maximum number of pointers to use when computing the velocity.
        // Note that the supplied MotionEvent may expose more than 16 pointers, but
        // at most |MAX_POINTERS| will be used.
        MAX_POINTERS = 16,
    };

    enum Strategy {
        // 1st order least squares.  Quality: POOR.
        // Frequently underfits the touch data especially when the finger
        // accelerates or changes direction.  Often underestimates velocity.  The
        // direction is overly influenced by historical touch points.
        LSQ1,

        // 2nd order least squares.  Quality: VERY GOOD.
        // Pretty much ideal, but can be confused by certain kinds of touch data,
        // particularly if the panel has a tendency to generate delayed, duplicate
        // or jittery touch coordinates when the finger is released.  This is the
        // default velocity tracker strategy.  Although other strategies are
        // available for testing and comparison purposes, this is the strategy that
        // applications will actually use.  Be very careful when adjusting the
        // default strategy because it can dramatically affect (often in a bad way)
        // the user experience.
        LSQ2,

        // The same as LSQ2, but reports 0 if the direction of the velocity returned
        // is sufficiently different from the primary direction of movement of the
        // touches contributing to the velocity.
        LSQ2_RESTRICTED,

        // 3rd order least squares.  Quality: UNUSABLE.
        // Frequently overfits the touch data yielding wildly divergent estimates
        // of the velocity when the finger is released.
        LSQ3,

        // 2nd order weighted least squares, delta weighting.
        // Quality: EXPERIMENTAL
        WLSQ2_DELTA,

        // 2nd order weighted least squares, central weighting.
        // Quality: EXPERIMENTAL
        WLSQ2_CENTRAL,

        // 2nd order weighted least squares, recent weighting.
        // Quality: EXPERIMENTAL
        WLSQ2_RECENT,

        // 1st order integrating filter.  Quality: GOOD.
        // Not as good as 'lsq2' because it cannot estimate acceleration but it is
        // more tolerant of errors.  Like 'lsq1', this strategy tends to
        // underestimate
        // the velocity of a fling but this strategy tends to respond to changes in
        // direction more quickly and accurately.
        INT1,

        // 2nd order integrating filter.  Quality: EXPERIMENTAL.
        // For comparison purposes only.  Unlike 'int1' this strategy can compensate
        // for acceleration but it typically overestimates the effect.
        INT2,
        STRATEGY_MAX = INT2,

        // The default velocity tracker strategy.
        STRATEGY_DEFAULT = LSQ2,
    };

    // Creates a velocity tracker using the specified strategy.
    // If strategy is NULL, uses the default strategy for the platform.
    explicit VelocityTracker(Strategy strategy);

    ~VelocityTracker();

    // Resets the velocity tracker state.
    void Clear();

    // Adds movement information for all pointers in a MotionEvent, including
    // historical samples.
    void AddMovement(const MotionEvent& event);

    // Gets the velocity of the specified pointer id in position units per second.
    // Returns false and sets the velocity components to zero if there is
    // insufficient movement information for the pointer.
    bool GetVelocity(uint32_t id, float* outVx, float* outVy) const;

    // Gets the active pointer id, or -1 if none.
    inline int32_t GetActivePointerId() const { return active_pointer_id_; }

    // Gets a bitset containing all pointer ids from the most recent movement.
    inline BitSet32 GetCurrentPointerIdBits() const
    {
        return current_pointer_id_bits_;
    }

private:
    // Resets the velocity tracker state for specific pointers.
    // Call this method when some pointers have changed and may be reusing
    // an id that was assigned to a different pointer earlier.
    void ClearPointers(BitSet32 id_bits);

    // Adds movement information for a set of pointers.
    // The id_bits bitfield specifies the pointer ids of the pointers whose
    // positions
    // are included in the movement.
    // The positions array contains position information for each pointer in order
    // by
    // increasing id.  Its size should be equal to the number of one bits in
    // id_bits.
    void AddMovement(const base::TimeTicks& event_time,
        BitSet32 id_bits,
        const Position* positions);

    // Gets an estimator for the recent movements of the specified pointer id.
    // Returns false if the pointer velocity is unknown.
    bool GetEstimator(uint32_t id, Estimator* out_estimator) const;

    base::TimeTicks last_event_time_;
    BitSet32 current_pointer_id_bits_;
    int32_t active_pointer_id_;
    scoped_ptr<VelocityTrackerStrategy> strategy_;

    DISALLOW_COPY_AND_ASSIGN(VelocityTracker);
};

} // namespace ui

#endif // UI_EVENTS_GESTURE_DETECTION_VELOCITY_TRACKER_H_
